Methods of making oxygen scavenging articles containing moisture

ABSTRACT

An extruded or molded article containing iron based oxygen scavenger, electrolytes, activated carbon, silica gel, or other water absorbing media, and optionally pore formers, is subjected to deformation to create voids or porosity, and subjected to water spraying or dipping to obtain a water activity of 0.4 or higher. The article is placed in a container or package containing oxygen sensitive articles.

BACKGROUND OF THE INVENTION

1. Technical Field

This disclosure relates to oxygen scavenging articles. Morespecifically, the disclosure relates to oxygen scavenging materialscontaining moisture and systems for and methods of making such articles

2. Description of Related Art

Flexible food packaging materials such as used to form a plastic pouchusually require good oxygen barrier properties in order to preventmicrobial growth and preserve the freshness of the food. This need canbe exemplified by packages such as those for beef jerky, sausages, andprocessed meats, among others. A sachet containing an oxygen scavengeris commonly used in these type food pouches to absorb the head spaceoxygen and to absorb any oxygen permeating through the package wall.Sachets have been used for some time in ready-to-serve food packages,but they have potential disadvantages and limitations. For example,sachets are generally comingled with the food product, and thus may beaccidentally ingested. Sachets also are susceptible to accidentalpiercing or cutting, which can lead to contamination of the foodproduct. And, sachets are not aesthetically pleasing. In addition,sachets are not generally suited for use in packaging liquid productsrequiring oxygen scavenging.

As one conventional alternative to using sachets, it is known to purgethe ambient air from a container and backfill the container with aninert gas, such as nitrogen. However, this process is costly and doesnot account for migration of oxygen into the package, for example, aftersealing the package.

Extruded articles containing oxygen scavengers in the form of film,tape, ribbon or strands are known and may be advantageous in somepackaging applications due to their powder-free construction andintegral, usually one-piece format. However, such articles are generallynot preferable in low-moisture applications, such as in packagingcoffee, because there is insufficient ambient moisture to facilitateabsorption of oxygen by the iron.

The following are documents identified by the inventor as relatinggenerally to oxygen scavenging:

U.S. Pat. No. 5,896,994, issued Apr. 27, 1999 to WR Grace for “SealedArticles,” relates to an oxygen scavenging film strip disposed in a traypackage containing oxygen sensitive articles.

U.S. Pat. No. 4,769,175, issued Sep. 6, 1988 to Mitsubishi Gas for“Sheet Like Oxygen Scavenging Agent,” describes mixtures of fiber, ironpowder, water, and electrolyte formed into a sheet-like product using apaper making process.

U.S. Pat. No. 4,317,742, issued Mar. 2, 1982 to Teijin for an “OxygenScavenging Composition, Heat-Generating Composition, And Heat-GeneratingStructure,” teaches a heat generating composition capable of scavengingoxygen.

In view of the above-described deficiencies in the art, and shortcomingsof the just-listed patents, there is a need in the art for an oxygenscavenger made from a film, tape or ribbon that contains a certainamount of moisture. There also is a need in the art for an oxygenscavenger having an adjustable amount of moisture therein, for example,such that the rate of oxygen scavenging in the container or package iscontrollable.

There also is a need in the art for an oxygen scavenging article thatdoes not occupy large spaces, is functional and is easy to dispense.

There also is a need in the art for an oxygen scavenger suitable foroperating at a water activity of 0.4 or lower, for example, as inconnection with food products such as powdery coffee and dry infant foodpowder. Of noted interest, for example, it is desirable to preservecoffee aroma or flavor for single serving ready-to-brew cups that areapproximately 30 cc or larger in volume. In a small food package, oxygenmay deteriorate aroma or flavor due to oxidation.

There also is a need in the art for a non-leachable oxygen scavenger,which will not change the taste of the articles with which the scavengeris packaged.

There also is a need in the art for a solution to one or more of theaforementioned products that is a sustainable solution using materialsof renewable resources and biodegradable in nature.

There also is a need in the art for an improved method of making anoxygen scavenger such as that described above.

SUMMARY OF THE INVENTION

The present invention remedies the foregoing needs in the art byproviding an improved oxygen scavenging material containing water thatcan be readily formed for inclusion in myriad packaging applications.

In one aspect of the disclosure, a method of making an oxygen scavengingmaterial includes stretching an oxygen scavenging material in at leastone axial direction to form pores in the material and wetting thestretched material with a liquid such that the pores in the materialretain a portion of the liquid.

The method may also include drying the stretched material after wettingto remove any moisture remaining on the surface.

In another aspect of the disclosure, a system for manufacturing anoxygen scavenging material includes a supply of oxygen scavengingmaterial, a tool for stretching the supply of oxygen scavenging materialin at least one axial direction, and a water supply for wetting thestretched oxygen scavenging material.

In another aspect, the system includes a dryer for drying the stretchedmaterial after wetting to remove moisture remaining on the surface.

In yet another aspect of the disclosure, an oxygen scavenger includes astretched oxygen scavenging film having a plurality of pores therein;and a liquid retained in the pores.

These and other aspects and features of the invention will beappreciated from the following disclosure and attached figures, in whichpreferred embodiment s of the invention are described and illustrated.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a flow chart illustrating a method of making a polymericfabricated oxygen scavenger including moisture.

FIG. 2 is a schematic representation of a system for creating an oxygenscavenging film containing moisture according to one embodiment of theinvention.

FIG. 3 is a schematic representation of a system for creating an oxygenscavenging film containing moisture according to another embodiment ofthe invention.

FIG. 4 is a schematic representation of a multi-cavity die-cut anddispensing apparatus which may be used in embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

As noted above, the disclosure relates generally to a method of makingpolymeric fabricated articles containing oxygen scavengers and moisture.FIG. 1 describes a manufacturing process 110 according to an embodimentof the invention. In step 112 of the process, a supply of an oxygenscavenging material is provided. The oxygen scavenging material can beprovided in many forms including but not limited to film, ribbon, andtape, and may be either in a packaged form for presentment, such as on aspool, or as a continuous web from machinery forming the material, suchas an extruder, mold, or the like.

The oxygen scavenging material may comprise any number of compositions.In one embodiment it includes an iron-based oxygen scavenger, aninorganic salt such as NaCl which forms an electrolyte in water, and amoisture absorber such as activated carbon, silica gel, molecular sieve,or clay. The oxygen scavenging material also optionally includes mineralparticles such as calcium carbonate as a pore former or a source ofinitiation of cavitation. When the oxygen scavenging material is formedas a ribbon, tape or film, it also includes a polymer such aspolypropylene, polyethylene, or polylactic acid. Those of ordinary skillin the art, when enlightened by this disclosure will understand thatother compositions of oxygen scavenging materials will be readilycompatible with the process, systems and articles described herein.

In step 114, the provided oxygen scavenging material is stretched toform pores therein. In one embodiment, the oxygen scavenging material isstretched axially in one or more directions, resulting in the desiredpore formation. For example, the film or sheet of oxygen-scavengingmaterial can be uniaxially stretched using conventional machinedirectional orientation tools. It can also be biaxially stretched bymachine directional orientation and transverse directional orientationtools to create voids or pores through deformation of pore formers. Thedraws ratio, defined as the ratio of the stretch length divided by theun-stretched length, can range from 1 to 100. The suitable draw ratiocan be experimentally determined to create porosity for the particularformulation chosen. The pore or void size can range from submicron to afew millimeter. It is preferably ranging from 0.1 to 500 micron, morepreferably ranging from 0.5 to 50 micron. The pores are preferablyevenly distributed across the articles. They can be isolated orinterconnected. They can be any shapes such as spherical, rectangular,triangular or multi-surfaced space. The pores can also be reticulatedstructure in which the open space is connected by fibrillated polymerstructure such as that commonly seen in filter papers or filtrationmembranes. Pores can also be cavitation or voids as initiated bydeformation around the included particles such as calcium carbonate ortalc. By varying the characteristics of the pores, such as theirmorphology, shape, size and number, the liquid retention properties ofthe material can be controlled. Although as just described in connectionwith the embodiment illustrated in FIG. 1 the pores are voids formed bystretching, pores may be naturally occurring in the oxygen scavengingmaterial, even without stretching. Pores are broadly understood to beany free volume in the oxygen scavenging material that is capable ofretaining a liquid, as will be described in more detail below.

In the embodiment of FIG. 1, the stretched and porous material is thenmoistened in step 116. The moisturizer may be any liquid, but in onepreferred embodiment is water. Other liquids used in the invention mayinclude water and alcohol mixtures, glycerin, water and glycerinmixtures, and solutions including water, such as electrolytic solutions.The moisturizing may be done by spraying, perhaps as a vapor, the liquidonto the stretched and porous material or by introducing the material toa bath containing the liquid.

When the porous material is moistened, the pores retain some of thatmoisture, even if the material is subsequently dried to remove surfacemoisture. The stretched, porous, moistened material is subsequently cutin step 118 to form oxygen scavenging articles. Each of the articles isplaced in a container requiring oxygen absorption in step 120.

The articles formed according to the process of FIG. 1 can beselectively manufactured to any number of specifications and for anynumber of uses. For example, the oxygen scavenging article may befabricated in the form of a packet, a ribbon, a strand, a ring, a flatfilm, a sheet, a label, or an insert for use in a coffee package, e.g.,a single-serve cup, such as a K-cup, bag, or container, to absorbresidual oxygen in the package. In other embodiments, the articles couldbe formed as lid stocks or sealing layers.

In another embodiment, the oxygen scavenging fabricated article isfabricated in the form of a packet, a ribbon, a strand, a ring, a flatfilm, a sheet, a label, or an insert stored with infant food to absorbresidual oxygen in the infant food package.

In fact, the invention is particularly useful in these applicationsbecause there is very little, if any, moisture in packages containingcoffee and infant food. The oxygen scavenger already contains moisture,so it will absorb oxygen under these circumstances.

The manufacturing process described with reference to FIG. 1 also can bealtered to provide desired results. For example, by controlling theamount of stretching, the porosity of the material can be varied, whichin turn varies the amount of moisture retained by the material. Theamount of moisture will have a direct impact on the rate of absorptionof the oxygen scavenging article.

Moreover, and as noted above, the oxygen scavenging composition may bemade according to many formulations, which can lead to variedperformance results. In one embodiment, the composition includes apolymer, an oxygen scavenger, a salt, a moisture absorber, and a poreformer. Additional components, such as surfactants also may be included.

Polymers useful for making the oxygen scavenging articles can includecommon polyolefins such as low density polyethylene, high densitypolyethylene, polypropylene, polystyrene, high-impact polystyrene,polycarbonate, polymethylmethacrylate and their derivatives orcopolymers. They also may include sustainable or biodegradable polymers,which generally include all common polymers generated from renewableresources and biodegradable polymers, such as polylactic acidcopolymers, starch-based polymers such as thermoplastics starch,polyhydroxyalkanoates, and polyhydroxybutyrate . Other biodegradablepolymers may be petroleum-based polymers such as polyethylene oxide orpolyvinyl alcohol.

The oxygen scavenger generally includes an iron powder. Morespecifically, the reduced iron powder preferably has 1-200 um meanparticle size, more preferably 5-50 um mean particle size and mostpreferably 10-40 um mean particle size. The iron can be mixed with saltor a combination of different electrolytic and acidifying components.The iron particles can also be coated with salt. The combination andrelative fraction of activating electrolytic and acidifying componentscoated onto the iron particles can be selected according to theteachings of U.S. Pat. No. 6,899,822, US Pat. applications 2005/0205841and 2007/020456, incorporated herein by reference. The coating techniqueis preferably a dry coating process as described in the referencesabove.

The salt can be any inorganic salt such as sodium-, potassium- orcalcium-based ionic compounds that are soluble in water. Typicalexamples include NaCl, KCl, Na₂HPO₄ and others. A mixture of separateelectrolytic and acidifying salt components can be advantageously usedin the formulation as described in prior art.

The oxygen absorbing composition preferably also includes a moistureabsorber, such as silica gel, activated carbon, molecular sieve, anothersorbent material, or a combination thereof. For example, a mixture ofthe materials may include activated carbon and silica gel in a 50/50mixture. The total loading can range from 2-80 wt %, preferably 5-60%,and more preferably 10-50%.

A pore former can also be used in the invention to promote formation ofvoids or pores during the stretching step. The pore former may be, forexample, CaCO₃, talc, Mg(OH)₂ , or some other mineral particle. Theloading can range from 10-70%, and preferably from 20-50%. Typically,pore formers can be compounded separately with resin as master batchesand fed into the extruder forming the polymeric oxygen scavenger. When amaterial containing a pore former is used, stretching of the oxygenscavenging material facilitates creation of micro-mechanicaldeformations around inorganic particles, such as around the pore former.

Surfactants also may be used in mixtures used to create the oxygenscavenger material. Some such surfactants useful for treating resinpellets or coated iron powders in order to maximize dispersion includelubricants such as mineral oil, fatty acids such as stearic acid, andlow molecular weight compounds such as waxes.

Fillers, modifiers, or other materials generally known in the polymerfilm-making art, such as elastomers, coloring agents, or the like, alsomay be incorporated into the oxygen scavenging material.

A smaller size of composite oxygen scavenging particles (limited bysmall particle sizes producing significant light scattering and haze infilms), comprising all necessary components for efficient oxidation,produces oxygen scavenging films with higher effective reactivity withpermeating oxygen and allows for a more efficient design of barrierstructures.

In addition, while mixtures according to the foregoing disclosure may beformed into a single layer film, barrier film reactivity is in someinstances advantageously improved by multilayer structural designs wherethe oxygen scavenging layer such as made according to the foregoingmixtures forms the middle layer of a three-layer structure made from thesame matrix resin. The specific optimal layer thickness ratios depend onthe overall film thickness and the oxidation kinetics of the activatedscavenger.

The three-layer film structure preferably has a layer ratio in the rangeof 49/2/49 and 1/98/1, with an optimum ratio, depending on the designtarget (such as the rate of headspace oxygen absorption) may be about40/20/40. The iron is preferably located in the middle of the threelayers. The outer layers may be any known oxygen permeable construction.

Films to be used as labels, laminates or inserts for a pouch may consistof single or multilayer structure with the coated iron uniformlydistributed in the film or in the chosen layer(s). For a multilayerstructure, the coated iron is preferably located in the middle of thestructure. It can be located adjacent to the external layer tofacilitate absorption. In other embodiments, a layered structureaccording to the invention may include an absorptive layer includingiron disposed on a backing or substrate, such as a PET substrate. Thesubstrate may be chosen for its aesthetics, for example, because it maybe more readily printed on or has an otherwise more desirable surfacecharacteristic. The substrate also may be chosen for its barrierproperties or for its ability to act as a removable layer, such as whenthe oxygen scavenger is an adhesive label. Handling may also dictate theuse and structure of the barrier layer.

FIG. 2 is a schematic representation of a system 200 for forming oxygenscavenging articles using a process similar to that described inconnection with FIG. 1. The system 200 generally includes a supply 210of an oxygen-absorbing polymeric material 212. In the illustration, thesupply 210 is a spool 211 about which the material 212 is disposed. Inother embodiments, the material 212 may be provided directly from themachine making the material, such as an extruder or mold.

In FIG. 2, the material 212 is provided as a continuous web fed from thespool 211 through a conveyance path. First, the material is acted uponby a stretching tool 214, which, as noted above, may be a conventionalMDO or TDO tool. Once stretched the material 212 is delivered, forexample, with the assistance of rollers 216, proximate a moisturizer218. The moisturizer 218 provides a liquid 220 to the material 212.Although only one moisturizer is shown in FIG. 2, disposed above thematerial 212 for moisturizing a top surface of the material, additionalmoisturizers could be present and placed in a multitude of locations,including beneath the material 212.

Once moisturized, the material 212 is conveyed to a cutter 222 that cutsthe material 212 into a plurality of discrete oxygen scavenging articles224. The oxygen scavenging articles 224 may be ready for use aftercutting, or they may undergo further processing. For example, as shownin FIG. 2, the articles 224 may be placed on a conveyor 226, driven by aseries of rollers 228, to be presented to a dryer 230 for removingsurface water. The conveyor 226 preferably transports the articles 224for direct packaging into a container in which oxygen is undesirable, orto a staging area, such as a bag, having limited oxygen. Once wet, thearticles 224 are active, so it is important to maintain them in alow-to-no oxygen environment until use.

FIG. 3 shows a system 300 slightly different from the system of FIG. 2.In FIG. 3, a continuous web of oxygen scavenging material 312 isprovided on a supply 310, which is a spool 311 in the illustratedembodiment. In this embodiment there is no stretcher and the oxygenscavenging material is fed, by a series of rollers 316 or the like, to amoisturizing bath 318 containing a liquid 320. The web of material isconveyed through the bath 318 while submerged in the liquid 320 to allowpores in the material or the material itself, e.g. by way of the silicagel or similar moisture retaining material, to retain some of the liquid320. Because the material is not stretched in the illustratedembodiment, the film may be required to be left in the bath 318 for a(relatively longer) time sufficient to allow the liquid to permeate theoxygen scavenging material 312 and occupy pores therein. In anotherembodiment the web may be stretched prior to wetting using an MDO or aTDO machine, as in the embodiment described in connection with FIG. 2.Whether stretched or not, the material used in these embodiments may bea single layer or a multi-layer, as described above.

The moistened material 312 is subsequently subjected to a dryer 330 toremove surface liquid remaining after the bath 318. Once dried, thematerial 312 is cut by a cutter 322 to form discrete oxygen scavengingarticles 324. After moistening, the oxygen scavenging material 312 isactive, so the articles 324 are preferably quickly cut and placed in asubsequently-sealed container 350. The container 350 may be thecontainer of ultimate use for the product, or may be an interimcontainer that is preferably oxygen-free so as to maintain efficacy ofthe article 324. Again, the wetted material may be a single layer,having a structure like that described above or some similar structure,or may have multiple layers.

Whether the material used is stretched or not, and whether a single ormultiple layers are used, the composition of the oxygen absorbing layermay be adjusted to achieve desired performance. For example, when thematerial is not to be stretched, additional silica gel or other similarwater retention material may be incorporated with the pore former beingreduced, even to the point of elimination. Similarly, the number ofpores can be varied by including more or less of the pore former. Poresize can also be increased by additional stretching of the material.

FIG. 4 is a schematic representation of the system in which the cutter322 is a die cutter that forms the discrete oxygen scavenging articles324 as circular discs from the moisture-retaining material 312. Asshown, a row of oxygen scavenging discs may be formed at the same time,and, although only one container 350 is shown, a plurality of containers350 preferably are arranged, each for receipt of one of the articles324.

The inventor also has conducted an experiment including aspects of theabove-described disclosure, which is described as follows:

Example 1 Preparation of Oxygen Scavenging Films Containing Porosity andMoisture Absorbers

A 15-mil film that contains an oxygen scavenger formulation was preparedby extruding a mixture of polypropylene, a modifier, iron, talc, andsilica gel. The polypropylene was a homopolymer commercially availableas Dow H110-02N. The modifier was a propylene-based elastomercommercially available from ExxonMobil as Vistamaxx™ VM6102, which canbe used with polypropylene to enhance its performance in certainapplications, such as in forming films. The iron was an iron and saltcombination made according to the teachings of U.S. Patent ApplicationPublication No. 2010/0255231 to Chau et al. for oxygen scavenging films,the disclosure of which is hereby incorporated by reference. The talcwas a commercially available talc sold by Luzinac as Jetfill 700 and thesilica gel was a commercially available silica gel having a 5 micronaverage particle size. The weight ratio for the mixture waspolypropylene/Vistamaxx/iron/talc/silica gel=25/25/10/30/10.

The mixture was extruded in a twin screw extruder at an averagetemperature of 250° C. for the extruder and die to form a 5-inch wide 15mil thick sheet. The sheet was collected on a winder. One-inch-widesamples were cut from the sheet and subsequently stretched using anInstron tensile tester at l/min strain rate to approximately 300%elongation, creating porosity or voids in the samples. The filmsappeared to show some stress-whitening and opaqueness after stretching.The film stripes were subsequently immersed in water for 30 min and, inthis experimental process, blot-dried briefly to remove the surfacewater. The wetted sample was found to have a water activity ofapproximately 0.7, different from the 0.4 of the unstretched, non-wettedfilm.

The samples were cut into one- to two-inch pieces and weighted toachieve approximately 3.5 gm for both the as-extruded and stretchedpieces. These cut pieces were tested for oxygen scavenging performanceusing a pouch test. More specifically, the cut samples were sealed in ahigh gas barrier bag and the bag was injected with 300 cc of O₂/N₂mixture to achieve a starting oxygen level of approximately 4.7-5%. Theoxygen absorption rate was measured using a MOCON PacCheck Model 450Head Space Analyzer at various times at room temperature. The oxygenabsorbed by the samples at these times is shown in Table-1. The datashowed that the stretched and stress-whitened samples had higherabsorption rate than the un-stretched, control film, despite both beingwetted.

TABLE 1 Oxygen absorption for the stretched films containing sorbentsand oxygen scavenger Film thickness Time O2 absorbed Sample mil hrscc/gm of film As extruded 14.5 0 0 14.5 1.04 24 1.69 48 2.64 Stretched13 0 0 14.5 1.71 24 2.55 48 3.49

The foregoing embodiments of the present invention are provided asexemplary embodiments and are presently best modes for carrying out theinvention. Modifications of these embodiments will be readily apparentto those of ordinary skill in the art. The invention is not intended tobe limited by the foregoing embodiments, but instead is intended to belimited only by the appended claims.

1.-25. (canceled)
 26. An oxygen scavenging material made by: stretchinga film containing an oxygen scavenger to obtain a stretched film; andwetting the stretched film with a liquid such that pores in the materialretain a portion of the liquid.
 27. The oxygen scavenging material ofclaim 26, wherein the film containing the oxygen scavenger comprises theoxygen scavenger, salt, as moisture absorber, and a polymer.
 28. Theoxygen scavenging material of claim 26, wherein the film containing theoxygen scavenger comprises a bonding agent.
 29. The oxygen scavengingmaterial of claim 26, wherein the film containing the oxygen scavengercomprises a pore former.
 30. The oxygen scavenging material of claim 26,wherein the film is extruded from a mixture of the oxygen scavenger, asalt, a moisture absorber, and a polymer.
 31. A sachet formed using theoxygen scavenging material of claim
 26. 32. An oxygen scavenging articleformed using the oxygen scavenging material of claim
 26. 33. The oxygenscavenging article of claim 32, formed as a packet, a ribbon, a strand,a ring, a flat film, a sheet, a label, an insert, lid stock, or asealing layer.
 34. The oxygen scavenging material of claim 26, whereinthe liquid is water.
 35. The oxygen scavenging material of claim 26,wherein the liquid comprises an alcohol and water mixture, glycerin, aglycerin and water mixture or an electrolytic solution
 36. An oxygenscavenging article comprising: a stretched oxygen scavenging film havinga plurality of axially-extending pores formed by stretching the oxygenscavenging film; and a liquid retained in the axially-extending pores.37. The oxygen scavenging article of claim 36, wherein each of theplurality of pores is sized generally between about 0.1 micron and 500micron across.
 38. The oxygen scavenging article of claim 36, whereinthe liquid is water.
 39. The oxygen scavenging article of claim 36,wherein the stretched oxygen scavenging film comprises a polymer, anoxygen scavenger, a moisture absorber, and a salt.
 40. The oxygenscavenging article of claim 36, further comprising at least one of apore former and a bonding agent.
 41. The oxygen scavenging article ofclaim 36, wherein the oxygen scavenger is one of a packet, a ribbon, astrand, a ring, a flat film, a sheet, a label, an insert, lid stock, ora sealing layer.
 42. The oxygen scavenging material of claim 26, whereinthe liquid comprises an alcohol and water mixture, glycerin, a glycerinand water mixture or an electrolytic solution